Only a relatively narrow shelf of soil and stone debris eroded from the slopes above separates the edge of the marsh from the base of Nā Pōhaku o Hauwahine. However, with the exception of a very small pool that forms partly beneath a tumble of boulders in rainy months, it is not immediately obvious that this is a wetland at all. A dense stand of California grass, neke or swamp cyclosorus (fern), and cattail forms a seemingly impenetrable wall of green more than head high. To one side, a large monkeypod shades a small part of the marsh, and to the other, hau trees line the "shore." Other than water-loving (aquatic) plants (see Kawai Nui vegetation), the fact that here at the base of the massive basalt boulders is Hawai`i's largest wetland becomes evident only upon venturing out into the dense growth of grass, fern, and cattail. With each step, the "ground" can be felt to give—not in a sinking manner like soft muck, but springy like a sponge, then further out like the bough of a tree—as if suspended above solid earth. The wai of Kawai Nui is located under a mat as thick as your lower leg is long of intertangled roots and decaying vegetation. So strong is the fiber of this mat, that little danger exists of getting wet while exploring in most parts of Kawai Nui. Beneath the mat, a thin layer of water, then mud. But the depth of the water layer increases steadily offshore, reaching perhaps 3 meters (10 feet) deep in some places.

The mat comes from and further supports the growth of aquatic plants, and these plants add to and bind the mat together. Under conditions of intense runoff, when the water rises but the mat can float no higher, flooding spreads across the vegetation surface. The actual relationship between mud bottom, water, and vegetation mat may be more complex than that; a subject just now under study. However, at least during all but the wettest months, open water in this marsh is limited to scattered ponds out near the middle of the marsh, drainage canals on the makai end, and stream channels where Maunawili and Kahana Iki streams enter at the mauka end where a floating mat does not develop. This fact is significant when considering the wildlife in the marsh for two reasons: first, water birds are only interested in vegetation which surrounds open water; and second, a thick cap covering the water surface results in an anoxic body of water beneath. That is, the water lacks oxygen since neither diffusion from the atmosphere or algal growth in the water are possible beneath the vegetation mat.

Marsh clearing at the base of Nā Pōhaku o Hauwahine, seen on May 5, 2000.

The hard work of numerous volunteers at Nā Pōhaku o Hauwahine includes clearing weedy plants, building trails, and planting native vegetation in an effort to restore this geological and cultural landmark on the margin of Kawai Nui Marsh. Someday this feature could be the jewel in a trail system circumnavigating the marsh. However, for the wetland here to become a significant educational resource, access to open water is necessary. So a part of the ‘Ahahui Mālama I Ka Lōkahiservice projects include clearing (by hand) the thick marsh vegetation and removing the floating mat over a small area below Nā Pōhaku o Hauwahine in order to restore open water habitat and create plots for growing native marsh plants.